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## Rapidity Gaps Between Jets at HERA and the Tevatron

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**Rapidity Gaps Between Jets at HERA and the Tevatron**Brian Cox Review of results from**A little bit of History**“The frequency of rapidity gaps between jets must be understood before these new physics signatures can be used” Bjorken Phys. Rev. D 47, 1(1993) “ Rapidity gaps between jets as a new physics signature in very high energy hadron hadron collisions” • How big are the strong interaction backgrounds? • What is the gap survival probability? BFKL will enhance the rate, but … “a subject beyond the scope of this paper and the competence of its author”**The first gaps between jets analysis from Tevatron and HERA**• ZEUS Collaboration: Phys. Lett. B369 (1996) 55. • D0 Collaboration: Phys. Rev. Lett. 76 (1996) 734. • CDF Collaboration: Phys. Rev. Lett. 80 (1998) 1156. • D0 Collaboration: Phys. Lett. B440 (1998) 189.**Overall agreement in gap fraction ~ 1% at Tevatron, ~ 10 %**at HERA • D0 – “BFKL ruled out”**Is BFKL really ruled out ?**B.C. Jeff Forshaw, Leif Lonnblad JHEP 9910 (1999) 023 , R. Enberg, G. Ingelman, L. Motyka Phys. Rev. Lett. B524 (2002) 273 The Mueller – Tang asymptotic approximation in numerator (and Mueller Navelet jet production in denominator) as implemented in HERWIG is not sufficient at Tevatron or HERA energies.**The new H1 and ZEUS measurements**Demanding ‘no energy’ in a rapidity region is not infra-red safe, and generates numerically important non-global logarithms • Run inclusive KT algorithm • All objects are included in jets • Gap event defined as : • Infra red safe definition of gap • Increases rapidity gap region • Reduces sensitivity to hadronisation effects • Reduces sensitivity to non-global logarithms G. Oderda and G. Sterman, Phys. Rev. Lett. 81, 3591 (1998) M. Dasgupta and G. P. Salam JHEP 0203 (2002) 017 R. B. Appleyby and M. H. Seymour JHEP 0212 (2002) 063**Energy Flow and Rapidity Gaps Between Jets in**Photoporduction at HERA Eur. Phys. J C24 (2002) 4, 517-527 http://jetweb.hep.ucl.ac.uk**Cross Sections and Gap Fractions as a function of x**Fractional longitudinal momentum of photon participating in the production of the two highest ET jets**Gap Fractions as a function of xp**Fractional longitudinal momentum of proton participating in the production of the two highest ET jets**Summary of the BFKL pomeron model**• CFL fit Tevatron data with s=0.17, gap survival = 0.2 • H1 fit data with s=0.18, gap survival not included in signal • ZEUS fit data with s=0.17, gap survival from JIMMY • Potentially large NLO corrections to BFKL not included at HERA, partially included at Tevatron (EIM) • H1 and ZEUS find that data not sensitive to underlying dynamics**Should the LHC listen more closely to Bjorken?**+ missing ET e.g. ATL-PHYS-2003-006 invisible